1. Field of the Invention
The present invention relates to an optical information storing apparatus which can handle different kinds of recording media.
2. Description of the Prior Art
As means for optically storing information, there have been known a writable optical disk of the DRAW type, a rewritable optical disk of the E-DRAW type, and an optical disk of the ROM type only for use of reproduction. For the DRAW type optical disk, the pits corresponding to the information to be stored are formed on the disk surface by a laser beam and the stored information is read out on the basis of a change in reflected light amount. For the E-DRAW type optical disk, flux reversal is caused on the disk surface due to the laser beam to record and erase information, and the recorded information is read out due to a magnetic Kerr effect or the like. For the ROM type disk, on one hand, the pits corresponding to information are preliminarily formed and the information signal is read out by use of a change in reflected light amount due to a laser beam.
Either one of those disks is selected in accordance with the purpose of information to be recorded. The ROM type disk is used in the case wherein information is preliminarily determined and mass production is needed and the disk must be preserved for a long time. The DRAW type disk is used in the case wherein the necessary number of disks is small and the disk must be preserved for a long time. The E-DRAW type disk is used in the case wherein there is a possibility such that the recorded information is erased later and the disk is used as a temporary buffer.
In this manner, the disks can be efficiently used. Even as for different kinds of disks, on the other hand, their fundamental constitutions for recording and reproducing information are substantially the same; therefore, it is desired to use a common driving apparatus.
In this case, however, depending on the kinds of disks, there are differences in reflection factor or transmission factor of the disk surfaces and in readout principle, so that the output level of the reproduced signal in the signal readout system, particularly, the information signal output component or the like changes by at least tens of times. In the case of reproducing information by the same reproducing system, there are problems such that an extensive dynamic range will be needed if the smaller reproduced signal is used as a reference, while noise will increase and the signal level will become too small for a small signal if the larger reproduced signal is used as a reference, and the like.
In addition, differences in reliability and error rate of the reproduced information signals occur dependent on the respective disks.
Namely, in the case of using the same error correction circuit for the respective disks, if the error correction circuit is constituted in accordance with the disk in which the error rate before correction is the highest, the over specification could be derived for the disk in which the error rate before correction is low. That is, since the error correction codes increase more than is needed for the information signal, the redundancy also increase more than is needed, resulting in poor coding efficiency.
A number of recording disks of various sizes (diameters) such as 30, 20, and 12 cm, or the like are used at present.
Those disks are used in accordance with the use object. The disk of a large size is used in the case of recording information of a large capacity. The recording disk of a small size is used in the case wherein easy handling property and portability of the recording disk are required.
Hitherto, the same recording/reproducing apparatus can use only one size of recording disk.
This is because of the following reasons. In the case of recording predetermined information in the recording disk using light, if the rotating speed of the recording disk is fixed to make constant the recording speed of the signal to be recorded, the diameter of this recording disk is proportional to the linear velocity, so that the length per unit (bit) of the information to be recorded is proportional to the diameter of the recording disk. Thus, the energy of light to be irradiated onto the unit area of the recording disk is inversely proportional to the diameter of the recording disk and the recording density in the disk is also inversely proportional to the diameter thereof.
Therefore, when the recording disk, having a diameter larger than that of the recording disk which is to be ordinarily used is used by the same optical information recording/reproducing apparatus, the light energy density on the recording disk is reduced, so that it can be difficult to properly record the information.
As described above, conventionally, only a single size of recording disk can be used in the same recording/reproducing apparatus. Therefore, in the case of using a plurality of recording disks of different sizes, there occurs a problem that a plurality of recording/reproducing apparatuses must be possessed corresponding to the sizes of the recording disks.